are often used in juice and beverage
processing operations. The magnets will
attract the piece of metal, preventing it
from potentially damaging a filler and
causing costly repairs and downtime.

And magnets can enhance product
quality. The advantage
of magnets is that
they will remove very,
very small pieces of
metal, such as rust
particles, whereas
metal detectors and
X-ray machines have
a finite detectability.

Two kinds of magnets
are used in food processing: ferrous magnets and rare-earth
magnets. Rare-earth
magnets are the stronger and more effective
of the two types of
magnets. They can remove fine metal dust
and work-hardened or
braided stainless steel.

There is also a range of formats that
allows magnets to be used in different
processing systems. These include grate,
tube, plate, liquid line, pneumatic, chute,
pipe and drum magnets. Each of these
different magnets has different applications and different product uses. Processors who do dry blending often install
grate magnets where bags are dumped to
remove metals at the start of the process.
Processors of dried fruit install plate magnets immediately before filling to remove
metal dust, specifically rust.

Magnets must be inspected and
tested on a regular schedule. If they are
used as a Critical Control Point (CCP),
they should also be validated. Most processors will mandate that in-line magnets be inspected and cleaned at least
once a day. As part of this process, they
often have the people performing these
activities collect what is on the magnet
and save it for future evaluation by the
quality staff.

Magnets should also be tested on aregular schedule to ensure that they areperforming properly. How often this isdone depends upon individual compa-nies. Equipment manufacturers recom-mend that this be done at least once ayear, but companies should conduct arisk assessment to establish a schedule fortheir own operations. Pull testing repeat-edly measures the hold-ing strength in ouncesof force or pounds at apredetermined distancefrom the surface or onthe surface of the mag-net itself. This may bedone by the equipmentmanufacturer or in-house. It is not a hardtest to learn how to do.Finally, magnets shouldbe validated to ensurethat they remove themetals being targeted. Ihave seen processors dothis by passing productspiked with a knownnumber of metal piec-es. They would thenlook at the magnet toverify that the metal was on the magnet.

Metal Detectors: Metal detectors are
designed to detect all metal in food
products above a certain size. The size
of metal that is detectable depends
upon the product and the package it is
in. There are different types of metal
detectors available to the food industry,
including systems that pass the products
through on a conveyor, in-line systems
for liquids and vertical inspection systems. Metal detectors are almost always
designed to reject product found to
contain metal, although there are occasional units in which the product
conveyor simply stops. Ideally, the best
location for a metal detector is after
packaging, which is why conveyor systems are so popular. If metal is detected,
the package will be rejected. Of course,
if the package itself contains metal
(common with packages made from
recycled materials), the processor might
want to consider adding another metal
detector to scan the packages themselves
prior to adding the food product. This
is, however, an expensive option.

Processors should work with the
equipment manufacturer to establish
minimum detection limits for the standards used with the unit. A processor
might demand that their suppliers pass
all products through a metal detector
that can detect the following standards:
1.0 mm ferrous, 1.5 mm nonferrous and
2.0 mm stainless steel. If the processor
is manufacturing hot dogs in a vacuum
package, the customer demands can
probably be met. However, if the goal is
to pass 20-pound boxes of frozen entrees
through the unit, that detection limit
will probably be impossible. Processors should obtain a letter from their
equipment manufacturer defining the
minimum detection limits for the unit.
Based on this letter, the processor should
obtain the necessary standards from the
equipment manufacturer, that is, a ferrous, nonferrous and stainless steel standard. For stainless steel standards, make
sure that the type of stainless in the standard reflects the primary type of stainless
in your plant and equipment. Processors
must also decide, based on risk, how often they should test their metal detectors
using these standards. At a minimum,
each standard should be tested at the
start and end of a product run with one
test during the middle of the run. In reality, most operations will conduct these
tests more frequently. Many operators
write their procedures so that testing is
at the minimum level noted above, but
in actual operations will test every 1 to
2 hours. Why? Because no auditor will
downgrade an operation for exceeding
testing levels.

There is an ongoing debate as to how
a company’s metal detector should be
incorporated into the organization’s
food quality and safety programs. Some
companies have determined that metal
detection should be a CCP in their
Hazard Analysis and Critical Control
Points (HACCP) plan, whereas others
deem it part of quality management
(prerequisite program). If the manufactured products are chopped or ground,
and the company’s Hazard Analysis
determines that there is a significant
potential for metal contamination, the